The invention relates to an apparatus for mixing and granulating powdered or granular substances with a drum-shaped evacuable vessel comprising a drive shaft arranged in the drum axis with mixing, stirring, and conveying devices, in which the vessel is oscillatable in the vertical plane containing the drum axis and is provided with a cylindrical sieve, or a sifting device which is concentrically housed in a cylindrical body attached to the vessel from the outside and communicates with the vessel in such a way that the lowest inner jacket lines of the vessel and of the cylindrical sieve form an angle of less than 20.degree. while a rotating discharge device is arranged inside of the sieve.
A plurality of procedural steps is required to produce a powdered material from several substances, as required for intermediate and final products in the pharmaceutical, food and cosmetics industries. Depending on the product, these steps comprise dosing, mixing, moistening, granulating, drying, and, in particular, sifting in order to achieve a certain grain size.
U.S. Pat. No. 3,946,996 discloses a general apparatus for mixing and granulating powdered substances which permits the execution of these procedural steps in one and the same apparatus, from mixing up to delivery of the granulate suitable for making tablets in a predetermined composition. There it proposes the attachment of a sieve of cylindrical form in a tubular body on the granulating drum, in which the axes of the circular-cylindrical sieve and of the granulating drum assume a determined angular relationship towards each other.
One problem of the sieve or the sifting device described in that patent is that it will communicate permanently with the interior of the drum after attachment.
For this reason, should the sifting device turn out to be superfluous or hindering while using the apparatus, even only temporarily, then the whole sifting device has to be removed and for instance, be replaced by a blind flange.
Also cleaning of the apparatus described in U.S. Pat. No. 3,946,996 is relatively expensive, requiring undesirable dismantling work.
It is the object of the present invention to improve the existing apparatus in such a way that the sieve or the sifting device can be easily separated from the drum from the outside, without a need for detaching the sifting device in which the entire apparatus should be easy to clean, including the sifting device.